1. Knowing basics of Process Safety
2. Having worked in process plants
3. Having a desire
In this part you become familiar risk reduction methods and how SIL can contribute to plant safety.
A Risk is the amount of harm that can be expected to occur during a given time period due to specific harm event. There is no such thing as zero risk. Therefore the concept of defining and accepting a tolerable risk for any particular activity prevails.
SIS achieves risk reduction by reducing the frequency/severity of the hazardous event. The amount of risk reduction achieved is indicated by the risk reduction factor (RRF):
RRF = probability of risk in state 1 / probability of risk in state 2
Layers of Protection
1. Basic Process Control System (BPCS).
2. Automated shutdown sequences in the process control system combined with operator intervention to shut down the process.
3. Safety Instrumented System (SIS). It is a safety system independent of the process control system. It has separate sensors, valves and logic system. No process control is performed in this system; its only role is safety.
4. Active protection layer such as valves or rupture disks designed to provide a relief point that prevents a rupture, large spill or other uncontrolled release that can cause an explosion or fire.
5. Passive protection layer like a dike or other passive barrier that serves to contain a fire or channel the energy of an explosion in a direction that minimizes the spread of damage.
6. Emergency Response Plan (ERP).
In this minute you get to know safety instumented system and its different components
The action of a Safety Instrumented System (SIS) is called a Safety Instrumented Function (SIF). More than one SIF may be assigned to a single SIS.
Now you get to know SIL assessment methods and and risk matrix
SIL Target Evaluation Study
According to IEC 61511, the semi-qualitative method of the calibrated risk graph enables the safety integrity level of a safety-related loop to be determined from knowledge of the risk factors associated with the process and basic process control system.
The approach uses a number of parameters, which together describe the nature of the hazardous situation when safety-related loops fail or are not available. One parameter is chosen from each of four sets, and the selected parameters are then combined to decide the SIL allocated to the safety-related loop. These parameters allow a graded assessment of the risk to be made, and represent key risk assessment factors.
Risk graph method is widely used for reasons outlined in section below. The risk graph and the descriptions of its four parameters and the ranges for each parameter are shown in Figure and Table below, respectively. This methodology can be applied for safety protection, environmental protection or asset protection. When the safety integrity level of a safety-related loop is assessed for different protections (safety, environmental and/or asset), the most conservative SIL target shall be chosen for this loop.
As risk graph method is a semi-quantitative technique it does not require precise hazard rates, consequences, and values for other parameters of the method. Hence, no special calculations or complex modeling is required. Moreover, it can be applied as a team exercise, similar to HAZOP, so that individual bias can be avoided. This way, all team members (e.g. from design, operations, and maintenance) will acquire a comprehensive understanding of process hazards and risks.
Another advantage of this method is fast conclusion process because it does not require a detailed study of relatively minor hazards and it can be used to assess many hazards relatively quickly. It is also useful as a screening tool to identify hazards which need more detailed assessment and minor hazards which do not need additional protection.
In this part the trainer investigates and compares two real case examples and determines the required SIL for each case based on risk matrixs.
Educational Institute for
Equipment and Process Design
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